This invention relates to sub-surface lifting methods for transporting or salvaging loads underwater. It provides significant practical and safety improvements over conventional lift bags and surface cranes.
Conventional lift bags employ an exhaust valve near the top of the bag which the user must manually vent when reducing lift or ascending. During ascent, if the exhaust valve does not vent the expanding air fast enough, (air expands, quadrupling in volume between 100 feet seawater and the surface), the load can accelerate upward out of control. By automatically venting the expanding air, the neutral bouyancy device, (NBD), eliminates any guesswork by the user, allowing him/her to concentrate solely on a controlled ascent, resulting in a safer operation. In addition, a conventional lift bag used by a scuba diver is often inflated by using the divers mouthpiece regulator and his/her own breathing air supply. The NBD precludes the risk of the diver removing the mouthpiece regulator from his/her mouth and conserves the limited supply of breathing air.
Lifting a submerged load with a surface crane presents practical problems which are overcome by use of the NBD. If the crane platform, (e.g. a boat or barge), is affected by surface swell, this movement is transmitted to the load. This situation often leads to sudden and dangerous loading and unloading of the crane as well as danger to the diver from sudden load movement. The NBD eliminates movement from these surface effects, even in shallow water. In addition, a crane must be positioned directly above the load. The NBD allows the user to transport the balanced load, both sideways and vertically, around and under obstructions. Expensive marine equipment time is also saved by not having to re-locate and re-anchor the crane platform.